Ever wanted to know what you could do with you old floppy disk drives, hard drives and scanners? Why don't you just turn them into a music instrument ;-)
Another interesting upcoming MIDI controller with built-in wireless support.
Fun to watch physics with magnets and marbles :-)
Bela, a project for an Embedded Platform for Low-Latency Interactive Audio, has now been fully funded. Might be a nice option for building your own audio device/instrument.
The NS1nanosynth seems to be a fun device, if you want to get into experimenting with a real analog modular synthesizer. There's also an experiment kit for even more fun :-)